STRUCTURE AND COMPOSITION 15 



of the fibre on its central axis, but are sometimes 

 in one direction and sometimes in another ; they 

 occur at irregular distances from one another and 

 vary in the degree of convolution. The number of 

 twists in a given length of the fibre is very variable, 

 and is increased by the exercise of care in the cultiva- 

 tion of the plant. The finer the diameter of the fibre, 

 the larger are the number of twists, and hence the 

 twists are most numerous in Sea Island cotton, which 

 is the finest variety yet produced. The presence of 

 the twist imparts a roughness to the fibres which 

 enables them to exert a certain amount of grip on 

 one another, and thus renders it possible for them to 

 be spun into a thread. Unripe cotton consists of 

 thin, transparent fibres with little or no twist. Such 

 fibres are known technically as " dead cotton/' and, 

 being very weak and brittle, they break up in the 

 processes of manufacture, thus increasing the amount 

 of waste, and also tending to weaken the yarn or 

 fabric into the composition of which they enter ; 

 they also possess the defect of not being able to take 

 dyes satisfactorily. For these reasons the presence 

 of much immature cotton reduces the commercial 

 value of the product. 



In chemical composition, cotton consists chiefly 

 (about 90 per cent.) of a comparatively pure form of 

 cellulose, together with about 7 to 8 per cent, of water, 

 0-4 per cent, of wax and oil, 0*6 per cent, of nitrogenous 

 substances, and i per cent, of mineral matter. The 

 wax is present as a thin layer on the surface of the 

 fibre and renders it incapable of absorbing water 

 readily. The oil appears to be identical with that 

 contained in the seed. In the preparation of the 

 so-called absorbent cotton wool which is used for 

 dressing wounds and for similar purposes, the wax and 

 oil are removed by boiling the fibre with a dilute 

 solution of caustic alkali under pressure ; the cotton 

 is subsequently washed and treated with bleaching 

 powder and hydrochloric acid, and again washed and 

 dried. The nitrogenous constituents of cotton consist 

 of the remains of the cell protoplasm and allied 

 substances. 



